So, i'm gonna buy a SM58 to record some vocals (pre-production, just messing around before we go into a studio). How big is the difference from a 58 to a 57 when it comes to guitar?
will it suck balls like a donkey, or be decent, just not optimal?
i have heard ppl say you won't hear the difference, and some say 58 for a guitar amp is just a nono....

it'll be mostly distorted tube amps btw (if that makes any difference)
I used to fiddle around a bit with these, I found out that the SM57 is a bit clearer than the SM58. SM58 sounds a little muddier to me.
Quote by Xplozive
You sir are a dick!
Quote by Toppscore
And then again, Wildthang, "You're probably NOT one of them clean Socialists, either"

the SM57 & 58 are actually the same microphone, the difference is the 58 has the silvery pop shield mesh over the microphone which makes it ideal for recording vocals. Obviously the pop shield may have a small impact on your guitar sound but I'm sure you will be able to compensate for it with a bit of EQ either with whatever recording program your using or by changing your amp settings (you may not need to at all).
My Gear:
Ashton AG131
Ashton GA10 (amp)
Marshall MG250DX (gasp, i know...)
Ibanez S470DXQM
EH Metal Muff
(")_(") ... he's gaining power
so is sm57 the way to go if you plan on recording mainly instruments? i plan on recording bass and guitar .. probably through my bass amp. but id like to do vocals sometimes as well. like acoustic+vocals is most likely case with vocals use.

so would 57 be better in my case?
It really doesn't matter, the 57 and 58 are basically the same mic. Many people say that the 58 is strictly a vocal mic and that the 57 is for instruments, but countless bands have used a 57 for vocals live and in the studio (i know New Order and The Clash have), and i'm sure many musicians have used a 58 for guitar cabs and such.

So you should just go with whatever you think looks cooler because it doesn't make a difference, but if you feel that you're going to be doing a lot of singing then it can't hurt to go for a 58 because of the wind shield.

EDIT: by the way, I use a 57 for recording practically everything and a good friend of mine uses a 58 for recording everything and we are both happy with our results.